Microscopic-measurement apparatuses such as infrared microspectrometers can acquire optical information from a minute portion on the surface of a sample. However, Fourier transform infrared spectrometers require integrated measurement data, even when measuring a single point. Additionally, to acquire optical information from every minute portion of a large measuring area, Fourier transform infrared spectrometers are also required to conduct mapping measurement in a position of a detector relative to the surface of a sample which is successively changed. For example, Japanese Unexamined Patent Publication No. 2006-208016 discloses a method of mapping measurement using an attenuated-total-reflection measurement apparatus, which can automatically conduct mapping measurement in a predetermined area.
As described above, however, when acquiring optical information from a multitude of measuring areas, it takes time to acquire integrated data in each measuring area, and it also takes a certain amount of time to acquire mapping data of a predetermined dimension.
Thus, a method which enables one to set several optical-information acquisition areas in advance, and set such areas at a single time, and then acquire data successively in every set area has been developed.
Generally, a position of a photoreceiver is successively moved relative to a position of a sample in a stepwise fashion during measurement. When several optical-information acquisition areas are set to be measured, it has been common that a stage where the sample is placed is moved according to movements between areas and relative movements within each area.
However, errors owing to movements accumulate as the stage is moved, and it is necessary to position a stage during mapping measurement to exactly the same place during area setting. Thus, an electrically-controlled stage with extremely high precision has been demanded. In addition, a stage is unsuitable for rapid scanning since it is generally heavy so as to maintain itself stable. Thus, it has been sometimes stressful for operators to set area positions with slow stage driving when setting optical-information acquisition areas.